Michael Prupas calls himself a “card-carrying liberal.” The Montreal television producer speaks proudly of his work with a one-time colleague, Pierre Trudeau, on the former prime minster’s authorized biopic. And, he says, he’s an admirer of the Kennedy family.

As such, it is in a tone that conveys bafflement that Mr. Prupas describes the campaign waged against his company’s production of a television miniseries on the Kennedys. The series has been called a “politically motivated smear job.” A propaganda film. A hit piece. The attention given John F. Kennedy’s sexual indiscretions, says Hollywood filmmaker Robert Greenwald, who has relentlessly criticized the production for the past year, amounts to “a disgusting, below-the-belt attack, both figuratively and literally.”

Mr. Greenwald’s pressure campaign has accomplished its main goal: getting the History Channel to walk away from its $15-million investment in the project starring Greg Kinnear as JFK and Katie Holmes as his wife, Jacqueline.

Mr. Prupas insists that The Kennedys, which will air in Canada in April, will leave viewers impressed with the family at its centre, and he says the claims of inaccuracies are unfair and overblown. And in a year in which two of the main Oscar contenders, The Social Network and The King’s Speech, are known to have taken liberties with actual events, is it unfair to expect a historical work to be anything more than “based on a true story?” This is John F. Kennedy, after all. It’s no secret that the man was a bit randy. “I don’t think there is anybody in North America, perhaps the world, who would argue with you if you said ‘Geez, did you know John Kennedy had extra-marital affairs?’,” says Mr. Prupas in an interview. “Or, ‘did you know Joe Kennedy was a bit of a bully?’”

The Kennedys was always intended to be a bold stroke for the History Channel in the United States. A specialty channel best known for grainy footage of long-ago wars, it committed two-and-a-half years ago to develop the miniseries with Mr. Prupas’ Muse Entertainment. By the end of 2009, scripts for the eight-hour series were complete, and History wanted to go ahead with the production. History would put up $15-million for its first foray into scripted drama; Muse would invest a similar amount. For Muse, the key to success would be selling broadcast rights internationally. That would require a big-name cast. “We were delighted to get Greg Kinnear,” says Mr. Prupas. Then came Barry Pepper (Saving Private Ryan) as Robert F. Kennedy and Tom Wilkinson (Michael Clayton) as the Kennedy patriarch. Finally, Katie Holmes signed on as Jackie. She brought something even more valuable from a sales standpoint: the tabloid sizzle of Mrs. Tom Cruise. “She was huge,” Mr. Prupas admits.

The casting process, though, had an unexpected side effect. Scripts made the rounds in Hollywood, and some people were not pleased by what they saw.

Mr. Greenwald, an activist filmmaker whose company, Brave New Films, has taken on the war in Afghanistan, U.S. health care corporations and Fox News, was particularly angered. Draft scripts he obtained included scenes during which JFK complained about his need for extra-marital sex. He made a crude analogy to his brother about sampling different things from a restaurant’s menu.

“They made it look like all the President cared about was sex and power and getting laid,” says Mr. Greenwald, in an interview from California. “It didn’t look like he cared about the country, or making a difference in the world, or anything like that. It was a hit job. A political hit job.”

Mr. Greenwald took the scripts to historians who questioned their accuracy. He filmed actors delivering the juiciest lines for a YouTube video. He recorded an interview with Ted Sorensen, a former Kennedy speechwriter, which became part of the same video on the Stop Kennedy Smears website.

Mr. Greenwald’s efforts resulted in a front-page story in The New York Times before filming had even begun. He pushed the History Channel to drop the project, which he called “politically motivated” because one of its producers is Joel Surnow, a conservative who is one of the co-creators of 24, the long-running series in which Jack Bauer displayed a rather Republican approach to counterterrorism.

Mr. Prupas, speaking from Montreal, calls the lobbying effort against the series “outrageous.” History Channel has its own historians to vet the scripts, and his company has lawyers approve them as well. “At the end of the day we got to the point where every single one of them was signed off on for historical authenticity by the historian,” he says.

But what is “authenticity,” exactly? When the History Channel historian gave approval to the scripts, “it was clear to everyone at that time that historical authenticity did not mean documentary production,” Mr. Prupas says, “What we were doing was a drama, which by definition was meant to compress the period we were covering into eight hours.”

Timelines are rejigged. Dialogue is invented — one can’t vouch for the accuracy of a conversation between JFK and Jackie when there was no one else in the room. Audiences understand that liberties are taken. Mr. Prupas cites recent works such as the miniseries John Adams, or the films Elizabeth or The Queen, all productions that fudged the historical record, at least a little. This month’s Academy Awards include two Best Picture nominees — The King’s Speech and The Social Network — that straddle the line between fiction and historical fact. The former glossed over King George VI’s early appeasement of the Nazis while the latter presents a depiction of the founding of Facebook that was described by the company’s CEO, Mark Zuckerberg, as “all this stuff that they got wrong, and a bunch of random details that they got right.”

As the producers of a drama, Mr. Prupas says, some corners must be cut. “Did we collapse timelines? Yes. Did we make up dialogue? Yes. But, did we have proof of the material events that we describe as having taken place? Yes, we absolutely did.”

Mr. Greenwald challenges that assertion, saying that “not a single reputable historian is willing to put his name to it.” Another New York Times story last month quoted unnamed sources as saying that History’s experts had concerns with the accuracy of the edited version of the series. And when History decided last month not to air the series, it issued a statement saying the production “did not fit with History’s brand,” a cryptic phrasing that many in the industry took to mean “inaccurate.” (It has declined to comment further.)

Mr. Prupas, however, insists that History’s expert gave him written approval of the scripts and verbal approval of the edited cuts of the series. If there are inaccuracies, he says, they are about times and dates — the kind of thing that might bother a serious historian but are commonplace in the film industry.

But while Mr. Greenwald has made an issue of what could be termed technical inaccuracies, he saves his real thunder for what he sees as the salaciousness of the production. Were it simply a matter of putting Jackie in Washington at a time when she was actually in Kennebunkport, it’s doubtful he would have engineered a year-long multimedia campaign.

Mr. Prupas believes the controversy comes down to image protection. “To be charitable to the Kennedy family that may be opposing this thing, I understand why they would like to preserve this image they have in their head of what their family was like.” (There have been reports that various Kennedy family members pressured History to drop the series, but Mr. Greenwald says he’s never been in contact with the family.)

“The shock to me,” Mr. Prupas says, “is that someone actually thinks that this show denigrates the Kennedy family. On the contrary, our feeling is that people will come away from the show having seen some of the warts in the family and say, ‘This is one incredible family.’ That’s what I feel and I think this is what our show shows.”

When this sentiment is relayed to Mr. Greenwald, he begins to laugh. Not a chuckle, but one of those roaring laughs that doesn’t suggest humour at all. He isn’t buying it.

After History backed away from The Kennedys, U.S broadcasts rights were shopped around. It didn’t find a home with HBO, FX, Starz or any of the more popular cable outlets — though an executive with the Showtime network told the Times that while he was passing on it, he couldn’t see what all the fuss was about — and instead ended up with Reelz, a little-known cable channel. It will air in more than 30 countries, including on Shaw Media’s History Television in Canada, in April.

Over at Stop Kennedy Smears, the most recent update decries Greg Kinnear’s support for the series, and directs readers to contact his publicist, “and tell her why a political smear is nothing to be proud of.”